1. Field of the Invention
The invention relates to a hydraulic tool and, more particularly, to a hydraulic fluid release system in a hydraulic tool.
2. Brief Description of Prior Developments
U.S. Patent Application Publication No. US 2003/0126905 A1 discloses a hydraulic pressing unit with an automatic hydraulic fluid release system that remains open until the ram is fully retracted. Manual hydraulic fluid release systems are also known in the art such as described in U.S. Pat. Nos. 4,947,672 and 6,564,610.
The subject invention can relate to hydraulic crimp tools and hydraulic cutting tools and the employment of an automated release valve that is pressure actuated. In detail, there is a need, but not limited to, an automatic release mechanism that after a predetermined pressure is reached, automatically retracts the crimp ram or cutting ram from the work piece.
There are other automatic retraction devices such as described in US2003/0126905 and U.S. Pat. No. 6,276,186. US2003/0126905 incorporates different mechanical or electrical latching devices to hold the non-return valve (relief valve) open. It incorporates mechanical latches and the relief valve (non return valve) is held opened until the ram is fully back which releases the valve to the closed position. Latching this valve open mechanical or electrically can gall and create metal galling and metal shavings that can easily contaminate the hydraulic circuit. The design in U.S. Pat. No. 6,276,186 is somewhat similar to many relief valves designs where the leading tip of the valve needle is conical and is of small area. When a predetermined pressure is reached the needle lifts and allows fluid to act on the larger secondary disc portion of the valve. In this patent the relief valve remains open until the ram is fully back to the rest position and pressure is near zero. This design requires the hydraulic fluid pass through the relief valve until the ram is fully back. This practice is common in the art. The secondary disc is sized such that the valve does not close until pressure is very low and, thus, full ram retraction or auto retraction. Traditional tool valves open and drop pressure to about 2000 psi. The valve then fully closes and the operator of the tool must actuate a mechanical release to retract the ram.